Single absorber layer radiated energy conversion device

ABSTRACT

A radiated energy to electrical energy conversion device and technology is provided where there is a single absorber layer of semiconductor material. The thickness of the absorber layer is much less than had been appreciated as being useful heretofore in the art. Between opposing faces the layer is about 1/2 or less of the carrier diffusion length of the semiconductor material which is about 0.02 to 0.5 micrometers. The thickness of the absorber layer is selected for maximum electrical signal extraction efficiency and may also be selected to accommodate diffusion length damage over time by external radiation.

Cross reference is made to the following copending applications that arein the general field of this invention: application Ser. No. 08/179,601filed Jan. 10, 1994 pending, of John L. Freeouf titled "Solid StateRadiation Detector" and application Ser. No. 09/034,430 filed Mar. 3,1998 pending titled "Multi Absorber Layer Radiated Energy to ElectricalEnergy Conversion Device" and assigned to the assignee of thisinvention.

FIELD OF THE INVENTION

the invention relates to a highly efficient, single semiconductorabsorbtion layer, radiated energy conversion device in which there isalso provision for accommodation for performance degradation resultingfrom exposure to external radiation.

BACKGROUND OF THE INVENTION AND RELATION TO THE PRIOR ART

In the conversion of radiated energy to electrical energy, it has beenthe practice in the art to use solid state semiconductor layerstructures that can produce hole-electron pairs that result from atomicparticles or photons, in passing through the semiconductor, engaging inprimary or secondary collisions with the semiconductor material. Theoppositely charged hole-electron pairs are extracted from the absorberand into external circuitry as a signal before they can recombine or betrapped in the semiconductor material.

The environment in which the conversion device is to be used also has amajor influence in the design. Use in the atmosphere, nominally Air Mass1.5 (AM1.5), usually takes place at room temperature in light with amoderate ultra violet (UV) content and minimal other energy radiation.Structural weight is of less concern. Use beyond the atmosphere, in AirMass 0 (AM0), involves a larger range of temperatures, structural weightis a serious consideration, the radiated energy, usually sunlight isintense with a larger UV content and operation is often in the presenceof significant external energy radiation. Structures for AM0 operationfrequently have features designed to "harden" or slow down deterioratingeffects of external radiation on the performance of the conversiondevice.

The single absorbtion layer type of radiated energy to electrical energyconversion device has the advantages of essentially unlimited breadth ofdevice area and relative simplicity in structural features and infabrication. There are however, in such a device, interrelatedstructural features that both produce and extract the electrical energytogether with reflective mechanisms that operate to get more than onepass out of the radiated energy in hole-electron pair production that,heretofore, in the art, required tradeoffs that had a limiting effect onefficiency and made control of radiation damage more difficult.

Among the influencing factors in the design of single absorbtion memberradiated energy to electrical energy conversion structures are: theabsorbtion lengths of the incident radiated energy in the semiconductormaterial, the compatibility of any radiated energy enhancement featureswith the extraction of the electrical energy, the attenuation of theradiated energy by the contacting structure and the compatibility of theoverall conversion device structure with manufacturing capability.

There has been activity in the art directed to single absorbtion membersemiconductor radiated energy to electrical energy converters. In U.S.Pat. Nos. 5,286,306; 5,342,455; 5,401,330; and 5,419,783 conversiondevices are described wherein structural features that are placed in theabsorber region of the absorbtion member for one purpose, interfere withor add complexity, with respect to another purpose. There is a need inthe single absorbtion member art for a radiation conversion device thatcan provide high efficiency achieved with structural and manufacturingsimplicity.

SUMMARY OF THE INVENTION

A radiated energy to electrical energy conversion device and technologyis provided where there is a single absorber layer of semiconductormaterial in a single absorbtion member that has a unique combination ofinterdependent features. The thickness of the absorber layer is muchless than had been appreciated heretofore in the art as being useful,and makes possible the use of lower quality semiconductor material.Between opposing faces the absorber layer is about 1/2 or less of thecarrier diffusion length of the semiconductor material. The opposingfaces of the absorber layer of semiconductor material are eachcompletely covered by a high electrical conductivity, low radiatedenergy attenuation, electrical conduction layer that extends to an edgeof the device for an electrical contact. There is a charge producingcarrier separation mechanism in the absorber layer between theconduction layers. The thickness of the absorber layer is selected formaximum electrical signal extraction efficiency and may also be selectedto accommodate diffusion length damage over time by external radiation.

The radiated energy to electrical energy conversion device is alsoprovided with an incident radiated energy enhancement and supportstructure positioned on the conduction layer on the incident radiatedenergy receiving face of the absorber layer and with a radiated energyinternal reflection mechanism positioned on the face of the absorberlayer away from the incident radiation that returns the energy thatpassed through the absorber for extra absorbtion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the features of the singleabsorber layer radiated energy to electrical energy conversion device ofthe invention.

FIG. 2 is a band energy diagram illustrating the internal chargeproducing carrier separation mechanism in the absorber layer.

FIG. 3 is a graph showing the electrical charge signal resulting fromproduction of a hole-electron pair in the absorber layer.

FIG. 4 is a radiation damage accommodating embodiment of the invention.

DESCRIPTION OF THE INVENTION

In accordance with the invention it has been found that the efficientabsorbtion of incident radiated energy in a single absorber layersemiconductor device is influenced by a greater number of interrelatedfactors in different ranges than had been appreciated and employedheretofore in the art. It had heretofore been accepted that since theradiated energy contains a distribution of photon/particles withdifferent energy content, in order to extract a practical amount ofenergy, it was desirable to have an absorber that had a thicknessapproaching the full carrier diffusion length. However, the closer tothe diffusion length assumed to be needed for thickness, the higher willbe the required quality of the semiconductor material. In contrast, inaccordance with the invention it has been found that most of theabsorbtion takes place essentially adjacent to the incident radiatedenergy entrant surface, that in such a thin region there is greatertolerance for semiconductor material defects, that there is a limit tothe amount of electrical energy that is extractable in the practicalsense, that additional absorber layer thickness distance beyond thatwhich is needed for maximum electrical extraction produces deleteriouseffects including heat, and that structural elements producing energyreflection in the absorbtion member should be outside the chargeextraction portion. In FIG. 1 there is shown the features of the singleabsorber layer radiated energy to electrical energy conversion device ofthe invention. The conversion device of the invention has, along thepath of the incident radiated energy, a structural capability before theincident energy entrant face that is devoted to maximizing the entrantenergy; there is a limited thickness, semiconductor absorber layerarranged for maximum collision event capture with full charge extractionof the resulting charge; and, there is a back reflection and scatteringmechanism positioned beyond the absorber layer. For clarity the absorberlayer will be described first.

Referring to FIG. 1 the incident radiated energy 1 is absorbed in aradiated energy to electrical energy conversion device 2 that has a flatabsorber layer 3 of semiconductor material between faces 4 and 5.Covering all of each of faces 4 and 5 and extending to the edge arethin, up to about one third the thickness 10 of the absorber 3, highelectrical conductivity conduction layers 6 and 7 each having a very lowattenuation of the radiated energy that passes through. There is anexternal electrical contact to each of conduction layers 6 and 7 fortransferring the extracted charge to integrating external circuitry,symbolically depicted as external contact elements 8 and 9. The absorberlayer 3 is of a selected, crystalline, amorphous, polycrystalline ororganic, semiconductor material with a bandgap in the range forabsorbtion of the energy photon/particle distribution in the incidentenergy. The thickness 10 of the material of the absorber 3 is related tothe diffusion length or distance a carrier produced by a collision eventwill travel during carrier lifetime. In accordance with this inventionthe layer 3 will have a thickness dimension 10 that is in the range of0.02 to 0.5 of a micrometer for the types of materials with anacceptable bandgap.

It should be noted that the semiconductor material used heretofore inthe art has been of the type known as high quality in which there areminimum carrier traps that could prevent a hole-electron pair formed inthe semiconductor material as a result of a photon/particle collisionfrom contributing to an output signal and that to have high quality,single crystal epitaxially grown material is usually needed. Incontrast, the structure of the absorber 3 in this invention is such thatevery collision produced carrier is within a fraction of it's diffusionlength from a conduction layer so that there is a substantial relaxationof any need for high quality semiconductor material.

In the absorber layer 3 a mechanism is provided that separatespositively and negatively charged carriers produced by the incidentradiated energy photon/particle collision events in the semiconductorabsorber layer 3 and produces a sweeping field that moves the carriersto the conduction layers 6 and 7.

In FIG. 2 there is shown a semiconductor energy band diagram thatillustrates the type of shift of the relationship of the Fermi level Efwith respect to the valence band edge Ev and the conduction band edgesEc that will produce the carrier separation mechanism and the resultingsweeping field.

In the energy band diagram of FIG. 2 a p region and an n region meet ata transition 11 with respect to the Fermi level defined by dashed lines,the separation of which varies under different structural arrangements.For example where there is a p and an n region meeting at a p n junctionthe separation could be as small as about 20 Angstroms (Å) whereas withan intrinsic region with a thin p layer or i-p junction formed at oneconduction layer and a thin n layer or i-n junction at the otherconduction layer, the separation could be essentially the absorber layerthickness 10.

The carriers, majority and minority, resulting from a collision event inthe absorber layer 3 produce a significant signal that has only a fewnanosecond duration.

Referring to FIG. 3 an example output signal, developed betweenterminals 8 and 9 of FIG. 1, is illustrated; and in connection withFIGS. 1 and 2; the signals from all the collision events occurring inthe absorber layer 3 are swept into the conduction layers 6 and 7 forsensing at terminals 8 and 9 and integrated into a steady state DCsignal in, standard in the art external circuitry, not shown.

The semiconductor material of the absorber layer 3 has a bandgap relatedto the spectral distribution of the photons/particles in the incidentenergy. If the bandgap is too large, too little energy will be absorbed.If the bandgap is too small, the maximum available output voltage willbe too small. In a single absorbtion member conversion device of thetype of this invention, the output voltage cannot be larger than thebandgap. Where the spectral distribution is of the order of that fromthe sun, which would be radiation essentially equivalent to that from a6000 degree Kelvin(K) black body, an optimum bandgap would be in aboutthe range of 1.4 to 1.5 electron volts (Ev); whereas where the spectraldistribution is of the order of that from an ordinary heating element;which would be radiation essentially equivalent to that from a 2000degree Kelvin(K) black body, an optimum bandgap would be in about therange of 0.4 to 0.7 electron volts (EV).

The semiconductor absorber layer 3 thickness 10 also takes intoconsideration an absorbtion distance through which the incident energymust pass in order that the desired photon/particles will be absorbed.Since the photon/particle energy distribution is not linear theabsorbtion distance will not be not linear.

In accordance with this single absorber layer radiated energy toelectrical energy invention the major portion of the absorbtion takesplace within a very short absorbtion distance and efficiency is greatestwhere the absorbtion distance thickness, element 10 of FIG. 1, of thelayer 3 is that at which maximum electrical charge extraction takesplace; which in turn is in a range up to about 1/2 the distance acarrier will travel in the semiconductor material during the carrierlifetime.

the thickness 10 of the absorber layer 3 may be viewed as beinginfluenced by opposing constraints and a selection will be a tradeoff.The layer must be thick enough for absorbtion, but in general, anysemiconductor material in which radiated energy can be absorbed, butfrom which electrical energy extraction cannot occur, should be kept toa minimum as it reduces efficiency. However, even though some addedthickness beyond that for which charge can be fully extracted with theamount of sweeping field that can be applied or obtained in a practicalsense does not add much to the output; some additional thickness maystill may be useful under some conditions.

The carrier extraction sweeping field can be achieved as described inconnection with FIG. 2 by the effect of hole-electron separation in thestructure. In a practical sense with the carrier separation sweepingfield in this invention the thickness 10 would be in the range of0.02-0.5 micrometer.

The absorber layer 3 material and thickness 10 are design considerationsthat can be optimized for specific conditions such as for narrowspectral energy distributions and for accommodation for devicedeterioration produced by radiation.

As a generalized example the diffusion length is about 3 micrometers forhole type carriers in high quality semiconductor materials GaAs and InP,so that an absorber layer 3 in those materials would have a thicknessdimension 10 that would be less than 1.5 micrometers.

In table 1 there is shown the transmitted power in relation toabsorbtion thickness for the materials Silicon (Si), Gallium Arsenide(GaAs) and Indium Phosphide (InP).

                  TABLE 1                                                         ______________________________________                                                      Thickness                                                         Material in micrometers Power                                               ______________________________________                                        Si            500        7.6%                                                    100 9.5%                                                                      10 19.5%                                                                      1 50%                                                                         0.1 77.9%                                                                     0.02 86.5%                                                                   GaAs 100 17.5%                                                                 10 17.6%                                                                      12                                                                            1 20.7%                                                                       0.1 50%                                                                       0.02 75%                                                                     InP 100 13.5%                                                                  10 14.1%                                                                      1 15.5%                                                                       0.1 44%                                                                       0.02 75%                                                                   ______________________________________                                    

As an illustration of the reasoning involved in the thickness dimensiontradeoff, for both GaAs and InP at 1 micrometer thickness about 95% ofthe AM0 power that will be absorbed by that material is in fact,absorbed. Where there is an increase in the thickness to 10 micrometers,there is an added 1% to 2% of the absorbed power but this smallpercentage gain is outweighed by the added electrical losses becauseeven if perfect, GaAs and InP will still have diffusion lengths of 3micrometers.

In the opposite direction of the tradeoff, going in the thinnerdirection, for InP at a thickness of 0.1 micrometer 64% of the totalaccessible power is absorbed, and for GaAs it is 60% for the samethickness. In other words in this invention over half the availablepower is absorbed in the first 0.1 micrometer of thickness 10 along theincident energy path through the entrant face 4. The absorbed powerroughly doubles between and 0.02 micrometer thickness 10 and a 0.1micrometer thickness 10 for both examples GaAs and InP. Correspondingly,if the electrical extraction efficiency from 0.1 micrometer of materialis more than half as efficient as it is from 0.02 micrometer of materialthere would be a gain in total power output by the increase inthickness. The gain however, decreases at greater thicknesses so thatthe tradeoff becomes more demanding. For example, for InP the powerabsorbed changes from 64% to 98% as the thickness 10 changes from 0.1micrometer to 1 micrometer. In the design tradeoff this thicknessincrease is worthwhile only if the electrical efficiency for powerextraction for 1 micrometer is more than 65% of that for 0.1 micrometer.For the example InP, this constraint is set initially, but in an AM0type application after exposure to 10¹⁶ 1 Mev electrons/cm² ofradiation, the carrier diffusion length will then have deteriorated to0.5 micrometer, so that having a thicker layer would no longer beeffective as an improvement.

In accordance with the invention the design considerations of theabsorber layer 3 material and thickness 10 in the structure of thedevice 2 provides a new ability to accommodate the deterioration of aconversion device resulting from use in the presence of extensiveexternal radiation such as occurs in AM0 conditions. The effect of thatexternal radiation is to reduce the diffusion length.

In table 2 the diffusion length of the materials Si, GaAs and InP isshown for radiation exposure per 1 MeV electrons/cm².

                  TABLE 2                                                         ______________________________________                                        Material                                                                        and Diffusion Length Radiation Exposure (1MeV electrons/cm.sup.2)           in micrometers                                                                             none    1e15    1e16  1e17  1e18                                 ______________________________________                                        Si           200     30      10    3     1                                      GaAs 3   0.1                                                                  InP 3   0.3 0.15                                                            ______________________________________                                    

Heretofore in the art in addition to the use of higher band gapmaterials, the principal approach to reducing the deterioration fromexternal radiation has been to provide shielding or hardening in orderto prevent the external radiation from getting into the moderately dopedportions of the structure. In this invention, essentially the onlymoderately doped region in the absorber 3 is in the charge separationmechanism. That region is very small, in fact it may be as small as thep-n transition region 11 of FIG. 2 which may, on a very abrupt p-njunction, be of the order of 20 Å across. The conversion device of thisinvention can operate effectively on very small diffusion lengths. Thiscapability can provide an accommodation for substantial externalradiation while the conversion structure still retains usefuloperability and efficiency. This feature of the structure of theinvention is highly valuable in heavy radiation applications because atthe 0.02 to 0.5 micrometer thicknesses of the invention electricalefficiency losses due to carrier diffusion length do not becomeimportant until much more massive degradation of the semiconductormaterial than has been seen heretofore in the art has occurred.

As an illustration, a state of the art device of InP or GaAs materialwould ordinarily have an absorbtion thickness of about the diffusionlength or about 3 micrometers and would provide about a 20% efficiency.In contrast, in accordance with this invention, if such a device, usingGaAs or InP as the semiconductor material and being equipped with anabsorber layer 3 of the invention with a thickness 10 of only 0.1micrometer, will still provide an efficiency of about 10%. If such adevice were to have InP as the semiconductor material and equipped withan absorber layer 3 of the invention with a thickness 10 of about 0.02micrometer, will still provide an efficiency of about 5%. In both casesit is assumed the diffusion length is greater than 0.3 micrometers. Thusthe structure of the invention will be more tolerant of lower qualitysemiconductor material and will have a much longer useful lifetime,under conditions where diffusion length is reduced under radiation, thanhas been seen heretofore in the art.

Were an external bias to be applied between terminals 8 and 9 fullcharge extraction over a greater distance would be possible but thatbias could not be so large as to produce junction break down.

It is to be noted that; in the structure of this invention, with therebeing an absorber layer only between 0.02 and 0.5 micrometers thick, andthat layer being completely covered on both faces 4 and 5 with highconductivity signal extraction material conduction layers 6 and 7; anelectrical extraction capability is provided in which any carrierresulting from any hole electron pair radiated energy collision event inthe absorber layer 3 needs at most a small portion of it's diffusionlength in travel to reach the contacting layers 4 and 5.

The materials suitable for the absorber layer 3 are semiconductors witha high enough band gap that thermally generated current does notsignificantly affect performance and that matches the power spectrum ofthe radiated energy being absorbed. The absorber layer 3 is produced ina thickness 10 range from about 0.02 to 0.5 micrometer and will requiredfurther processing for a support member 12 and energy entrant efficiencyelement 13 on one surface and an energy reflection mechanism 14 on theother surface. The absorber layer 3 can be grown using the Metal OrganicChemical Vapor Deposition (MOCVD) technique standard in the art. Whichtechnique provides very good control of layers in the desired thicknessrange and very reproducible devices. The growth process involves the useof vapor phase chemicals such as phosphine for the anion source andtri-methyl indium for the cation source. The gasses are passed over ahot substrate in a range of from 600 to 750 degrees C. where they reactto form the compound desired. Growth rates of 10 to 200 nanometers perminute at a pressure of 0.1 to 1 atmosphere, with an inlet ratio ofV/III of about 10 to 500, may be used.

The structure of the invention, being based on a design principle whereimproved output is achieved from material considered to be of poorquality, the design will also improve efficiency in cases where thematerial is of poor quality for reasons different from radiation damage.For instance where the growth operation takes place on a latticemismatched substrate, such as GaAs on sapphire or InP on Si, which leadsto material with a substantial density of misfit dislocations, and acorrespondingly small carrier diffusion length. While this situationwould impact the efficiency of a device that required the full diffusionlength the structure of this invention would be minimally affected if atall.

Among the approaches for use of the thin layer after it's removal fromthe substrate, the most convenient is to metallize the free surfaceemploying a grade pattern for light transmission, bond the metallizedsurface to a transparent substrate, remove the original substrate byetching the sacrifical layer, metallize the back surface which is nowexposed using a transparent metal with a rough surface followed by ahighly reflective metal. As another approach the free surface could becoated with a transparent metal with a rough surface followed by ahighly reflective metal then bond to a substrate that does not need totransmit light for example metal, then remove the original substrate byetching the sacrificial layer followed by metallization using a grid forlight transmission. Both approaches now have a single exposed surface towhich another substrate can be bonded.

The absorber layer 3 is grown on a sacrifical, etch responsive layer, ona substrate. On the incident energy side, the conduction layer 6 is thendeposited, followed by the positioning of a supporting cover of theorder of about 200 micrometers thick of glass 12. The sacrifical layerand substrate are then removed by etching thereby exposing the face 5.Thereafter, the conduction layer 7 is applied on the face 5 followed bythe reflection mechanism 14. As examples; for GaAs a sacrificial layerof AlGaAs grown on a GaAs substrate would be used with an HF etchant;for InP a sacrificial layer of InGaAs grown on a InP substrate would beused with an HCl etchant.

In accordance with the invention the radiated energy to electricalenergy conversion device has all structural features pertaining to entryof the incident energy on the entrant face of a thin film controlledthickness absorber layer and all energy reflection features on theremaining face of the absorber layer. The absorber layer 3 withconduction layers 6 and 7 can also be used as one independent absorbtionmember in a serial incident radiation path device, that may have manyother absorbtion layers.

Returning to FIG. 1, the incident radiation 1 is in a form that has beenconcentrated as is standard in the art. The conversion device has anelement 12 positioned between, a standard in the art, antireflectioncoating 13 and the conductive layer 6. The element 12 provides supportfor the thin device structure, and can be a glass over or a transparentoxide of silicon or sapphire of the order of about 200 micrometers inthickness to which the up to 1/2 micrometer thickness absorber may beattached or grown.

Further in FIG. 1, beyond the conductive layer 7 of the absorber 2, inthe incident radiation path, there is provided a reflection mechanism 14for providing multiple passes through the absorber of the radiatedenergy. The reflection mechanism 14 includes a highly reflective coating15, such as silver, positioned on a transparent oxide or metal layer 16that is about 2.0 micrometers in thickness and with a roughenedreflection capability depicted as element 17 such as would be producedby sputtering or by laser ablation and positioned between the layer 16and the highly reflective coating 15. In operation in the reflectionmechanism, the highly reflective coating 15 returns most of the energyback into the absorber for continued absorbtion passes. The roughenedreflection capability 17 further causes many angular internal reflectionenergy passes that operate as energy trapping. Overall the reflectionmechanism adds a 50% increment to the efficiency.

In FIG. 4 an embodiment of the principles of the invention is shown thataccommodates substantial radiation damage thus exhibiting a much longeruseful lifetime than has been seen heretofore in the art for use undersimilar intense radiation conditions.

Under AM0 conditions there is a region known as the Van Allen belt thatis around 3200 kilometers above the earth where the radiation exposureis so intense that a conventional radiated energy to electrical energyconverter would only have a useful life of the order of days. Theradiation level in the Van Allen belt heretofore has caused the poweringof communication satellites by radiated energy conversion to be confinedto altitudes above the earth of about 700 kilometers in order for theconverters to have a practical useful lifetime. However, at such a lowaltitude there would be required three times as many satellites as wouldbe needed if it were possible to have a radiated energy to electricalenergy converter that had an acceptable useful lifetime that wouldoperate in the Van Allen belt. Through the principles of the inventionthe embodiment of FIG. 4 provides a radiated energy to electrical energyconversion device that has a useful life of a decade in the radiationintensity of the the type encountered in the Van Allen belt.

The semiconductor material of the absorber is InP, which although it hasbeen used heretofore in radiated energy to electrical energy conversiondevices, with this invention a slower diffusion length deterioration inthe presence of intense radiation property is of advantage.

Referring to FIG. 4, where the same reference numerals as used inearlier figures are used where appropriate, the incident radiatedenergy, which for this AM0 application is solar photon energy, islabelled element 1 and is incident over the area of an antireflectionlayer 13 that in turn is on a glass support layer 12. The device 2 ismade up of a an absorber layer 3 of Indium Phosphide (InP) on whichthere is a first conduction layer 6 on a first face 4 and there is asecond conduction layer 7 on a second face 5. The conductive layer 6being in contact with the support layer 12. The absorber 3 is made up ofa high conductivity, doped to about 1×10²⁰ per cm³, n+ layer 3A that isabout 100 Å thick, separated from a high conductivity, doped to about1×10²⁰ per cm³ p+ layer 3B that is about 100 Å thick, by an essentiallyintrinsic low conductivity layer 3C, that is doped to about 1×10¹³ percm³ p-, and that is in the range of from about 1000 Å to about 2800 Åthick that serves the function of the region 11 of FIG. 2. Together thelayers 3A, 3B and 3C provide the charge separation mechanism of thedevice. In contact with the conduction layer 7 is a photon reflectingand trapping mechanism 14 made up of a transparent metal or oxide 16,such as SnO or InSnO, the back side of which is abraded and is depictedas roughened element 17, then covered by a highly reflecting metal layer15, such as Ag. The overall combined thickness of layers 3A, 3B and 3Ccorresponding to dimension 10 of FIG. 1 is designed when built at thebeginning of life (BOL) to be within the range of 0.02 to 0.5micrometers which in turn is between 1/3 and 1/2 of the diffusion lengththat will occur after exposure in orbit to the expected radiation forthe duration to the time of the projected end of the life (EOL) of theconversion device. For example assuming a goal to be survival of theconversion device in -10¹⁷ 1 Mev electrons/cm²⁻ radiation until thediffusion length deteriorates to 1/2 the value in table 2, or 0.15micrometers for InP. It will be apparent that design at BOL will beinitially such that there will be a tradeoff of significant energy lostthrough the absorber film at BOL that is offset by extended EOL.

In assembling the device, after bonding the absorbtion region grown on asacrificial layer of InGaAs on GaAs, to the cover glass support layer,there may be a need for a blocking agent such as black wax to protectthe cover glass and the interface during separation of the InGaAs byetching in HCl.

What has been described is the structure and fabrication of a singlelayer radiated energy to electrical energy conversion device where anabsorber layer thickness is selected for maximum electrical extraction,lower quality semiconductor material is tolerated, and accommodation isavailable for selected useful life duration under radiation.

What is claimed is:
 1. A radiated energy to electrical energy conversiondevice wherein radiated incident energy is introduced into a supportedsingle absorber layered structure in an incident energy path that isessentially perpendicular to the layers of said layered structure,comprising serially in combination along said incident energy path:anabsorber of semiconductor material,said absorber having,first and secondessentially flat parallel surfaces and a thickness that is in a rangefrom 0.02 to 0.5 of a micrometer, a first high conductivity low energyattenuation conduction layer extending across all of said first surfaceof said absorber, a second high conductivity low energy attenuationconduction layer extending across all of said second surface of saidabsorber, a carrier separation mechanism in said absorber between saidfirst and said second high conductivity low attenuation conductionlayers, and, an external electrical output connected to each of saidfirst and second high conductivity low attenuation conduction layers. 2.The radiated energy to electrical energy conversion device of claim 1wherein said carrier separation mechanism is across a p-n junction insaid absorber of semiconductor material.
 3. The radiated energy toelectrical energy conversion device of claim 1 wherein said carrierseparation mechanism is across an intrinsic conductivity region betweenhighly doped p and n regions of said absorber of semiconductor material.4. The radiated energy to electrical energy conversion device of claim 1wherein said carrier separation mechanism is across an intrinsicconductivity region of said absorber of semiconductor material formingan i-p junction at said first conduction layer of said absorber and i-njunction at said second conduction layer of said absorber.
 5. Theradiated energy to electrical energy conversion device of claim 1wherein said first and second high conductivity low energy attenuationconduction layers are high extrinsic conductivity doped portions of saidsemiconductor absorber.
 6. The radiated energy to electrical energyconversion device of claim 1 wherein each of said first and second highconductivity low energy attenuation conduction layers is of metal and isabout one third the thickness of said absorber.
 7. The radiated energyto electrical energy conversion device of claim 1 wherein saidsemiconductor material is at least one of crystalline, amorphous,polycrystalline and organic material.
 8. The radiated energy toelectrical energy conversion device of claim 1 wherein saidsemiconductor material is a material taken from the group consisting ofSi, GaAs and InP.
 9. The radiated energy to electrical energy conversiondevice of claim 1 wherein said radiated energy in said incident energypath passes through a transparent support layer of a material taken fromthe group consisting of sapphire, silicon oxide and glass beforeentering said absorber.
 10. The radiated energy to electrical energyconversion device of claim 1 further comprising a reflection mechanismpositioned in said incident energy path after said incident energy haspassed through said second high conductivity low energy attenuationlayer of said absorber.
 11. The radiated energy to electrical energyconversion device of claim 10 wherein said reflection mechanismcomprises a highly reflecting layer positioned in said incident energypath after said incident energy has passed through said second highconductivity low energy attenuation layer of said absorber.
 12. Theradiated energy to electrical energy conversion device of claim 11wherein said reflection mechanism further comprises a roughenedreflection and trapping layer positioned between said absorber and saidhighly reflecting layer.
 13. A radiated energy to electrical energyconversion device wherein radiated incident energy is introduced into asingle absorber layered structure in an incident energy path that isessentially perpendicular to the layers of said layered structure,comprising, along said incident energy path, the serial combination of:atransparent support layer of a material taken from the group consistingof aluminum oxide, silicon oxide and glass, an absorber layer of InPsemiconductor material,said absorber having first and second essentiallyflat parallel surfaces and a thickness that is in a range of 0.02 to 0.5of a micrometer, said absorber further having three layersrespectively,a first layer of high conductivity, low energy attenuation,conduction material of p+ conductivity about 100 Å thick and doped toabout 1×10²⁰ per cm³, positioned on and extending across all of saidfirst surface of said absorber, a second layer of intrinsicconductivity, about 1000 Å to 2800 Å thick, doped to about 1×10¹³ percm³, positioned in contact with said p+ layer, and a third layer of highconductivity, low energy attenuation, conduction material of n+conductivity, about 100 Å thick, doped to about 10²⁰ per cm³, positionedin contact with said intrinsic second layer, and extending across all ofsaid second surface of said absorber, said three layers providing thefunction of a carrier separation mechanism in said absorber, an externaloutput connected to each of said high conductivity low energyattenuation layers, and, a reflection mechanism, for reflecting backinto said absorber, energy that has passed through said third layer ofsaid absorber, said reflection mechanism comprising a roughenedreflection and trapping capability layer positioned in contact with thethird absorber layer and a highly reflecting layer positioned in contactwith said reflection and trapping capability layer.
 14. In a radiatedenergy to electrical energy conversion device wherein radiated incidentenergy is introduced into a layered absorber structure in an incidentenergy path that is essentially perpendicular to the layers of saidabsorber, the improvement comprising, along said incident energy path,the serial combination ofa support layer of a material taken from thegroup consisting of aluminum oxide, silicon oxide and glass, an absorberlayer of semiconductor material taken from the group of Si, GaAs andInP,said absorber layer having first and second essentially flatparallel surfaces and a thickness that is in a range of 0.02 to 0.5 of amicrometer,a first high conductivity low energy attenuation conductionlayer extending across all of said first surface of said absorber layer,a second high conductivity low energy attenuation conduction layerextending across all of said second surface of said absorber layer, acarrier separation mechanism in said absorber between said first andsaid second high conductivity low attenuation conduction layers, anexternal electrical output connected to each of said first and saidsecond high conductivity low attenuation conduction layers, and, areflection mechanism, for reflecting back into said absorber, energythat has passed through said second high conductivity low energyattenuation conduction layer of said absorber, said reflection mechanismcomprising a roughened reflection and trapping layer positioned incontact with said second high conductivity low energy attenuationconduction layer and a highly reflecting layer positioned in contactwith said reflection and trapping layer.